Methods for producing a tunable vertical cavity surface emitting laser

ABSTRACT

Methods are disclosed for producing a tunable vertical cavity surface emitting laser (VCSEL) using photonic crystals and an electrostrictive material that includes a hologram with a narrow filter function. Photonic crystals are formed such that the active region of the VCSEL is bounded by the photonic crystals. The photonic crystals have a periodic cavity structure that reflects light of certain wavelengths through the active region of the VCSEL such that laser light at the wavelengths is generated. The periodic cavity structure includes a central defect that does not include any cavities. The single mode is emitted through the central defect. The electrostrictive material that includes a hologram makes the VCSEL tunable because the shape of the electrostrictive material changes when an electric field is applied. The filter function of the hologram thus changes as well in response to the electric field such that the VCSEL is tunable.

RELATED APPLICATIONS

[0001] This application is a continuation, and claims the benefit, ofU.S. patent application Ser. No. 10/253,100, entitled A Tunable VerticalCavity Surface Emitting Laser, filed on Sep. 24, 2002, and incorporatedherein in its entirety by this reference.

BACKGROUND OF THE INVENTION

[0002] 1. The Field of the Invention

[0003] The present invention relates to tunable vertical cavity surfaceemitting lasers. More particularly, embodiments of the present inventionare concerned with methods for producing a tunable vertical cavitysurface emitting laser that uses an electrostrictive polymer having aholographic optical element with a narrow filter function.

[0004] 2. Background and Related Art

[0005] Vertical cavity surface emitting lasers (VCSELs) are an exampleof semiconductor lasers that are used in optical fiber systems. VCSELshave several advantages over other types of semiconductor lasers. VCSELscan be manufactured in large quantities due to their relatively smallsize and can often be tested on a single wafer. VCSELs typically havelow threshold currents and can be modulated at high speeds. VCSELs alsocouple well with optical fibers.

[0006] VCSELs typically emit wavelengths on the order of 0.85 microns.VCSELs that operate at single wavelengths or at longer wavelengths onthe order of 1.3 to 1.55 microns, which are more useful in opticalcommunications systems, are very difficult to manufacture or fabricate.The difficulty in fabricating VCSELs that generate light in a singlemode and/or at longer wavelengths is often related, for example, to theatomic lattice structure of the materials, the quality of the activeregion or gain medium, the reflectivity of the mirror systems, and thematerial composition.

[0007] Another problem with VCSELs is related to their tunability.Tunable semiconductor lasers are very useful, especially inwavelength-division multiplexing (WDM) systems. When fixed wavelengthlasers are used in WDM systems, it is necessary to have a separate VCSELfor each wavelength. For example, a 100 channel WDM system requires 100different VCSELs. This leads to a number of different problems frommaintaining an adequate inventory for spare parts to producing andtesting VCSELs of varying wavelengths. A tunable laser can alleviatemany of these expensive issues.

[0008] In general, tunable lasers often suffer from needing a long gaincavity in order to generate sufficient gain. From a tuning perspective,the long cavity is extraneous and complicates the tuning functionalitybecause the modes of the gain cavity, for example, must be kept in afixed relationship with respect to the tuning element. Thus, manytunable lasers require a phase adjust section. VCSELs have the desiredshort cavities, but the gain for single mode VCSELs is insufficient toallow generation of optical power in the multi-milliwatt range.Increasing the diameter of the VCSEL aperture to increase power alsoresults in multi mode emission.

BRIEF SUMMARY OF AN EXEMPLARY EMBODIMENT OF THE INVENTION

[0009] These and other limitations are addressed by the presentinvention, which relates to a tunable vertical cavity surface emittinglaser that emits a single mode. The single mode is emitted by forming aphotonic crystal in the VCSEL that is highly reflective for certainwavelengths. As a result, only the reflected mode(s) achievesappreciable gain in the active region of the VCSEL. The photonic crystalalso includes a central defect for propagation of the emitted light. Thetunablity is achieved by forming an electrostrictive material on theVCSEL. A reflection hologram or holographic optical element (HOE) with anarrow filter function is included in the electrostrictive material. Thecentral wavelength of the HOE can be tuned by applying an electric fieldor voltage to the electrostrictive material. Advantageously, the tunableVCSEL can emit a single mode over a tunable range and higher power atlonger wavelengths.

[0010] In one embodiment of the present invention, a photonic crystalwith a central defect is formed on the upper DBR layers of a VCSEL, or aperiodic cavity structure is formed directly in the DBR layers.Alternatively, the DBR layers are omitted and the photonic crystal withthe central defect is formed directly on the active region. Thereflectivity of the photonic crystal is dependent on the wavelength ofthe light and on the angle of incidence. The photonic crystal providesthe necessary reflectivity such that a single mode is reflected throughthe active region, which results in stimulated emission of photons atthe corresponding wavelength of the incident photon. Usually, thecentral defect corresponds to an aperture through which the laser lightis emitted from the VCSEL.

[0011] After the photonic crystal is formed, a tuning element is alsoformed on the photonic crystal. The tuning element is anelectrostrictive polymer that includes a reflection hologram or HOE witha narrow filter function. The electrostrictive polymer undergoesdimensional changes when an electric field is applied and the centerwavelength of the HOE is thereby tunable. The HOE also has highreflectivity and the DBR layers may be omitted in one embodiment.

[0012] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to describe the manner in which the above-recited andother advantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

[0014]FIG. 1 is a perspective view of a photonic crystal or layer with aperiodic cavity structure;

[0015]FIG. 2A illustrates a vertical cavity surface emitting laser withan electrostrictive filter where the mirror layers are formed fromphotonic crystals and/or DBR layers;

[0016]FIG. 2B illustrates an electrostrictive filter that is formed on amirror layer that includes a photonic crystal and Distributed BraggReflector layers;

[0017]FIG. 2C illustrates an electrostrictive filter that is formed on amirror layer that only includes a photonic crystal;

[0018]FIG. 2D illustrates an electrostrictive filter that is formed on amirror layer where the periodic cavities have been formed directly inthe upper DBR layers;

[0019]FIG. 2E illustrates a mirror layer that only includes anelectrostrictive filter with an embedded holographic optical element;

[0020]FIG. 3 illustrates that the cavities or holes formed in thephotonic crystal can have different depths and that the cavities canextend into other layers of the vertical cavity surface emitting laser;

[0021]FIG. 4 illustrates a top view of a vertical cavity surfaceemitting laser that includes a photonic crystal with a lattice or cavitystructure that defines a central defect that does not include anycavities; and

[0022]FIG. 5 illustrates a vertical cavity surface emitting laser wherethe cavities formed in the photonic crystal extend into the activeregion and are surrounded by a semi-insulating material in the activeregion.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

[0023] Vertical cavity surface emitting lasers (VCSELS) are some of themost common light sources used in fiber optics. At a basic level, VCSELsare essentially pn-junctions that convert electrical energy into lightenergy. Typically, a gain medium or active region is formed at thepn-junction between the p-type semiconductor material and the n-typesemiconductor material. The active region often includes quantum wellsthat can be either compressively or tensile strained quantum wells. Theactive region may also include quantum dots.

[0024] In VCSELs, mirrors or mirror layers are formed both above andbelow the active region. The mirrors reflect light or photons back andforth the through the active region of the VCSEL. Within the VCSELcavity that is effectively bounded by the mirrors or by this mirrorsystem, the light resonates vertically or perpendicularly to thepn-junction. Because the light is resonating vertically, the cavitylength of a VCSEL is often very short with respect to the direction oflight travel. The length of the cavity thus has an effect on the abilityof a photon to stimulate the emission of additional photons,particularly at low carrier densities. Some of the light escapes themirror system and emerges from a surface of the VCSEL

[0025] The mirrors or the mirror system of a VCSEL must be highlyreflective and this high reflectivity requirement cannot be achievedthrough the use of metallic mirrors. VCSELs currently employ DistributedBragg Reflector (DBR) layers. DBR layers are formed by forming orgrowing alternating layers of semiconductor or dielectric materialswhose refractive index varies. Light is reflected at the junctions ofthese alternating layers and in order to achieve the high reflectivityrequired by VCSELs, many layers must be formed or grown as previouslydiscussed.

[0026] The present invention relates to vertical cavity surface emittinglasers that can be tuned to emit single modes at various wavelengthsincluding longer wavelengths that are more suitable for opticalcommunication systems. VCSELs structured as described herein also havethe advantage of being able to generate increased power in a singlemode. These and other advantages are achieved by forming the mirrorsystem or mirror layers of VCSEL using photonic crystals or using acombination of DBR layers and photonic crystals. In one embodiment, thephotonic crystal includes a central defect. In another embodiment, anelectrostrictive material that includes a holographic optical element orreflection hologram in included in the VCSEL.

[0027] A photonic crystal is a material that has a cavity or holestructure formed therein that is reflective for certain wavelengthswhile other wavelengths are not reflected. In other words, thereflectivity of photonic crystals is wavelength dependent and theparticular wavelength(s) reflected by a photonic crystal is oftenrelated to the cavity or hole structure of the photonic crystal. FIG. 1illustrates an exemplary photonic crystal or layer. A material becomes aphotonic crystal when a plurality of cavities or holes that are periodicin nature are formed or structured therein, as illustrated by thephotonic crystal 100. Thus, any material, including DBR layers, arereferred to herein as photonic crystals when a periodic cavity or holestructure is formed therein.

[0028] Cavities 102 and 104 are examples of the cavities that are formedin the photonic crystal 100. Each cavity typically passes through thephotonic crystal 100. It is also possible for the cavity structure to beformed such that the photonic crystal 100 is not perforated by cavities.In another example, the cavities pass completely through the photoniccrystal and extend into other layers of the VCSEL. The cavities areformed or drilled in the photonic crystal 100 using, for example,electron lithography. The distance between cavities in the cavitystructure affects the wavelength of laser light that is emitted by theVCSEL. In one example, the photonic crystal 100 enables VCSELs togenerate wavelengths on the order of 1.3 to 1.55 microns in a singlemode at higher power. Power can be increased by enlarging the aperturethat is formed, in one example, by oxidizing some of the DBR layers.

[0029] The wavelength(s) emitted by a VCSEL can be altered by changingcharacteristics or attributes of the photonic crystal. Characteristicsor attributes that can be changed such that a VCSEL emits a differentwavelength(s) include, but are not limited to, the periodic cavitystructure (rhombic cavity structure, square cavity structure, triangularcavity structure, hexagonal cavity structure, and the like), the shapeof the cavities (circular, square, triangular, and the like), the angleof the cavities with respect to the surface of the photonic crystal, thedepth of the cavities, the material from which the photonic crystal isformed, the thickness of the photonic crystal, the size and shape of acentral defect in the photonic crystal, and the like or any combinationthereof. The reflectivity of the photonic crystal is also dependent onwavelength and incident angle. Thus, a VCSEL with a photonic crystalemits a single mode and the wavelength of the emitted mode is related tothe photonic crystal.

[0030]FIG. 2A is a block diagram that illustrates generally thestructure of a VCSEL in accordance with the present invention. The VCSEL200 begins with a substrate 202. A lower mirror layer 204 is formed orgrown on the substrate 202. An active region 206 is next formed or grownon the mirror layer 204. On the active region 206, an upper mirror layer208 is grown or formed. As the mirror layers 204 and 208 repeatedlyreflect light or photons through the active region 206, the laser light210 is ultimately generated and exits the VCSEL 200 as laser light 210.An electrostrictive filter is often included as an additional layer inthe upper mirror layer 208 or as a separate layer. The electrostrictivefilter includes a HOE or a reflection hologram with a narrow filterfunction. The VCSEL 200 is tunable because the central wavelength of theHOE or the reflection hologram changes as an electric field is appliedto the electrostrictive filter.

[0031] The active region 206 is typically formed from a semiconductormaterial. The mirror layers 204 and 208 can be formed from or includephotonic crystals or layers. The photonic crystals provide thereflectivity required by the VCSEL 200 and are not as difficult to growas the multiple DBR layers previously discussed. Employing photoniccrystals in the mirror layers of a VCSEL makes VCSELs easier tofabricate and reduces cost. In addition, VCSELs that emit differentwavelengths of light can be fabricated on the same wafer by controllingthe cavity structures or other attributes of the photonic crystals.

[0032] The photonic crystals can be formed, for example, from GaAs,AlGaAs, InGaAs, InP, GaInAsP, AlGaInAs, InGaAsN, InGaAsSb, and the like.The photonic crystals can also be formed from dielectric materials thatcan be deposited in a thin film. The material used to fill the cavitiesalso extends to similar materials, although the cavities are oftenfilled with air. The resonance frequency of the photonic crystal can bealtered or changed if the refractive index of the material used to formthe photonic crystal and/or fill the cavities is tunable.

[0033]FIG. 2B illustrates an exemplary mirror layer 208. In FIG. 2B, themirror layer 208 includes the DBR layers 250, the photonic crystal 251and an electrostrictive filter 256. The mirror layer 208 is formed onthe active region of the VCSEL. In this example of the mirror layer 208,the number of DBR layers required to attain sufficient reflectivity isreduced because of the reflectivity of the photonic crystal 251. Areflection hologram or HOE 258 embedded in the electrostrictive filter256 also contributes to the reflectivity of the mirror layer 208.

[0034]FIG. 2C illustrates another example of the mirror layer 208, wherethe DBR layers are absent and only the photonic crystal 260 and theelectrostrictive filter 266 are present. As previously stated, thephotonic crystal 260 provides the reflectivity required by a VCSEL,although the HOE 268 embedded in the electrostrictive filter 266 mayalso contribute to the reflectivity. Both FIG. 2B and FIG. 2C illustratecavities 252 and 261 that have been formed in the photonic crystals 251and 260, respectively. The cavities 252 and 261 are formed before theelectrostrictive filters 256 and 266 are formed.

[0035]FIG. 2D illustrates another example of the mirror layer 208. Inthis example, the cavities 272 are formed directly in the DBR layers270. The electrostrictive filter 274 with an included HOE 276 is thenformed on the DBR layers 270. In FIG. 2E, the mirror layer 208 onlyincludes the electrostrictive filter 280 that includes a HOE 282. Thereflection hologram 282 provides the requisite reflectivity of theVCSEL. The mirror layer 208 illustrated in FIGS. 2B, 2C, 2D, and 2E canalso be used as the mirror layer 204 of the VCSEL 200 shown in FIG. 2A.

[0036] In each example where a photonic crystal includes a periodiccavity structure, a central defect has also been formed. In each case,the central defect does not include any cavities, but is surrounded bythe periodic cavity structure. FIG. 2B illustrates a central defect 253,FIG. 2C illustrates a central defect 262, and FIG. 2D illustrates acentral defect 276.

[0037]FIG. 3 illustrates another example of a VCSEL 300 thatincorporates photonic crystals in a mirror layer of a VCSEL. In thisexample, the lower mirror layer of the VCSEL 300 is formed from DBRlayers 304. The upper mirror layer of the VCSEL 300 is a combination ofthe DBR layers 308 and a photonic crystal 310. As previously stated,when photonic crystals are included as part of the mirror layers, thenumber of DBR layers 308 can be reduced or omitted completely.

[0038]FIG. 3 also illustrates that the cavities formed in the photoniccrystals can have depths that extend into other layers of the VCSEL 300.For example, the cavity 312 is limited to the photonic crystal 310, thecavity 314 extends into the DBR layers 308, the cavity 316 extendscompletely through the DBR layers 308, the cavity 318 extends into theactive region 306, and the cavity 320 extends into the lower DBR layers304. The depth of the cavities that are formed in the VCSEL 300 can varyand typically have an impact on the mode that is emitted by the VCSEL300. In one embodiment of a VCSEL, all cavities are typically formed tosubstantially the same depth. For example, all of the cavities mayextend into the active region. In another embodiment, the depth of thecavities can vary. After the cavities are formed in the VCSEL 300, theelectrostrictive filter is formed.

[0039]FIG. 4 is a top view of a VCSEL whose structure includes aphotonic crystal with a central defect. Typically, the cavities of thephotonic crystal are formed in the VCSEL after the photonic crystal hasbeen formed as a thin film on the active region or DBR layers. Thecavities or holes are then drilled using, for example, electronlithography or other lithography technique. FIG. 4 illustrates that thecavities formed in the VCSEL 400 have been formed, in this particularexample, using a square cavity structure 406. The cavities can be formedusing other cavity structures as well.

[0040] A central defect 402 is formed by not drilling or formingcavities or holes in a portion of the photonic crystal. The latticestructure of the cavities or holes surround, in this example, thecentral defect 402. In other words, the central defect 402 does notinclude any cavities or holes. In one embodiment, the central defect 402permits the single mode to propagate through the photonic crystal.Because of the wavelength dependence of the reflectivity of the photoniccrystal, the VCSEL lases at a single mode. In addition, the emitted modemay have a wavelength on the order of 1.3 or 1.55 micrometers, althoughthe present invention is not limited to these wavelengths. By increasingthe size of the aperture and/or the central defect 402, the power of theVCSEL 400 can be increased without emitting additional modes.

[0041]FIG. 5 illustrates a cross section of a tunable VCSEL 500. In thisexample, the mirror layer only includes the DBR layers 508. The cavitieshave been formed directly in the DBR layers 508. Thus, the DBR layers508 can be referred to as a photonic crystal. The photonic DBR layersinclude a central defect 516 that is surrounded by cavities that extendthrough both the DBR layers 508 and the active region 506, and into thelower DBR layers 504. To prevent surface recombination of carriers wherethe cavities 512 traverse the active region 506, semi-insulating regions514 have been grown in the active region. In one example, thecomposition of the semi-insulating regions 514 is FeInP. Anelectrostrictive filter 510 has been formed on the photonic DBR layers508. The electrostrictive filter 510 includes a reflection hologram orHOE 518. Finally, a contact 520 is formed on the electrostrictive filter510.

[0042] After the active region has been formed on the lower DBR layers504, the semi-insulating regions 514 are formed in the active region.The semi-insulating regions 514 are formed where the cavities 512 willbe formed. Next the photonic crystal 506 is formed on the active regionthat includes the semi-insulating regions 514 and 516. Finally, thecavities 512 are drilled in the DBR layers 508, through thesemi-insulating regions 514 in the active region 506 and into the lowerDBR layers 504. Thus, the cavities 512 are drilled such that thecavities penetrate the previously formed semi-insulating regions 514 and516. In this manner, the effects of surface recombination of carriers isreduced or eliminated.

[0043] As previously stated, the electrostrictive filter 510 includes areflection hologram or HOE 518 with a narrow filter function. The HOE518 is a diffractive element that includes a fringe system. The fringesof the HOE 518 are parallel to the surface of the VCSEL. The centerwavelength of the HOE can be tuned by applying an electric field to theelectrostrictive filter 510. As the electrostrictive filter 510 changesshape in response to the electric field, the narrow filter provided bythe HOE shifts. This provides a free spectral range that the VCSEL cantune. In one embodiment, the free spectral range is on the order of 40nanometers, which is sufficient to not require phase adjustment.

[0044] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A method for producing a tunable vertical cavity surface emitting laser, the method comprising: forming a substrate; creating a lower mirror layer on the substrate; creating an active region on the lower mirror; and creating an upper mirror layer on the active region, and at least one of the upper and lower mirror layers comprising at least one photonic crystal produced by: depositing at least one layer of material on an adjacent layer; and defining a plurality of cavities in the at least one layer of material so that a periodic structure is formed.
 2. The method as recited in claim 1, wherein creating the lower mirror layer on the substrate comprises one of: forming the lower mirror on the substrate; or, growing the lower mirror on the substrate.
 3. The method as recited in claim 1, wherein the plurality of cavities are defined in the at least one layer of material using a lithography process.
 4. The method as recited in claim 1, wherein both the upper and lower mirror layers comprise at least one photonic crystal.
 5. The method as recited in claim 1, wherein the plurality of cavities is defined such that a substantial number of the cavities perforate, at least, the at least one layer of material.
 6. The method as recited in claim 1, wherein the plurality of cavities is defined such that a substantial number of the cavities extend only partially into the at least one layer of material.
 7. The method as recited in claim 1, wherein the periodic structure is formed such that the photonic crystal is reflective for at least one selected wavelength.
 8. The method as recited in claim 1, wherein the at least one layer of material comprises a plurality of DBR layers.
 9. The method as recited in claim 1, wherein creating an upper mirror layer on the active region comprises: creating a photonic crystal on the active region; and creating an electrostrictive filter on the photonic crystal.
 10. The method as recited in claim 9, wherein the cavities of the photonic crystal are defined prior to creation of the electrostrictive filter on the photonic crystal.
 11. The method as recited in claim 1, wherein depositing at least one layer of material on an adjacent layer comprises depositing a dielectric film on the adjacent layer.
 12. The method as recited in claim 1, wherein the at least one layer of material includes at least one of the following: Al; In; Ga; As; Sb; and, N.
 13. The method as recited in claim 1, wherein the active region substantially comprises a semiconductor material.
 14. The method as recited in claim 1, wherein creating the active region on the lower mirror layer comprises one of: forming the active region on the substrate; or, growing the lower mirror on the substrate.
 15. The method as recited in claim 1, wherein creating an upper mirror layer on the active region comprises: creating a plurality of DBR layers on the active layer; creating a photonic crystal on an upper DBR layer; placing an electrostrictive filter on the photonic crystal; and placing a reflection hologram on the electrostrictive filter.
 16. The method as recited in claim 15, wherein the cavities of the photonic crystal are defined prior to creation of the electrostrictive filter on the photonic crystal.
 17. The method as recited in claim 1, wherein a substantial number of the cavities of the photonic crystal have substantially the same depth.
 18. The method as recited in claim 1, further comprising defining a central defect in the at least one photonic crystal.
 19. The method as recited in claim 17, wherein the central defect comprises a portion of the photonic crystal substantially free of cavities.
 20. The method as recited in claim 1, wherein definition of the plurality of cavities results in the substantial definition of a central defect in the at least one photonic crystal.
 21. The method as recited in claim 1, further comprising filling at least some of the cavities of the photonic crystal.
 22. The method as recited in claim 21, wherein filling at least some of the cavities of the photonic crystal comprises filling at least some of the cavities with a tunable material.
 23. The method as recited in claim 21, wherein filling at least some of the cavities of the photonic crystal comprises filling at least some of the cavities with one or more of: dielectric material; Al; In; Ga; As; Sb; and, N.
 24. A method for producing a tunable vertical cavity surface emitting laser, the method comprising: forming a substrate; creating a first plurality of DBR layers on the substrate; creating an active region on one of the first plurality of DBR layers; forming a plurality of semi-insulating regions in the active region; creating a second plurality of DBR layers on the active region; and defining a plurality of cavities, each of the plurality of cavities passing through the first and second plurality of DBR layers as well as through a corresponding semi-insulating region of the active region.
 25. The method as recited in claim 24, wherein each of the cavities is defined such that the portion of the cavity passing through the corresponding semi-insulating region is substantially surrounded by semi-insulating material.
 26. The method as recited in claim 24, wherein the semi-insulating material substantially comprises FeInP.
 27. The method as recited in claim 24, wherein a depth of each semi-insulating region is substantially coextensive with a thickness of the active region.
 28. The method as recited in claim 24, wherein the plurality of cavities are formed by drilling.
 29. The method as recited in claim 24, wherein the plurality of cavities at least partially defines boundaries of a central defect in each of the first plurality of DBR layers and the second plurality of DBR layers.
 30. The method as recited in claim 24, wherein the plurality of cavities is defined such that a periodic structure is formed in each of the first plurality of DBR layers and the second plurality of DBR layers.
 31. The method as recited in claim 24, wherein the plurality of cavities of the photonic crystal are formed through the semi-insulating regions such that the active region includes a lattice structure of semi-insulating rings.
 32. The method as recited in claim 24, further comprising creating a tunable element on one of the second plurality of DBR layers.
 33. The method as recited in claim 32, wherein creating a tunable element comprises creating an electrostrictive polymer filter including one of: a reflection hologram; and, a holographic optical element (HOE).
 34. The method as recited in claim 32, further comprising forming a contact on the tunable element.
 35. The method as recited in claim 32, wherein creation of the tunable element occurs subsequent to definition of the plurality of cavities.
 36. A method for producing a tunable vertical cavity surface emitting laser, the method comprising: forming a substrate; creating a lower mirror layer on the substrate; creating an active region on the lower mirror; creating an upper mirror layer on the active region, at least one of the upper and lower mirror layers comprising a photonic crystal; and creating a tunable element on the upper mirror layer.
 37. The method as recited in claim 36, wherein a mirror layer that comprises a photonic crystal is created by defining a plurality of cavities in the mirror layer comprising the photonic crystal so that a periodic structure is formed.
 38. The method as recited in claim 37, wherein the plurality of cavities is defined such that a periodic structure is formed in the photonic crystal. 